The absorptive mechanism for iron in the small intestine will be studied using primarily in vitro physiological and biochemical techniques. Special emphasis will be placed on the isolation of mucosal iron binding compounds and evaluating their role in mucosal iron metabolism. Techniques for the isolation of saline soluble as well as particle bound iron compounds will be developed. Electrochemical techniques will be used for the estimation of stable iron in order to determine the specific activity of the 59Fe used in labeling the fractions isolated. Various species and mutants (rats, mice, sex-linked anemic mice) will be used in these studies. In addition, varying physiological states of iron absorption will be studied in order to correlate absorption with any apparently significant iron compound that is isolated.